1. Field of the Invention
The present invention relates to an improvement in a power transmitting silent chain apparatus for use as a timing chain for power transmission in an automobile, a power transmitting chain in an industrial machine or the like.
2. Description of the Related Art
In a conventional power transmitting silent chain apparatus, a silent chain comprises a plurality of link plates each having a pair of teeth profiled as shown in FIG. 5 hereof so that it starts meshing with a sprocket at outer flanks 15 forming outer sides of the link teeth 14. Inner flanks 16 forming inner sides of the link teeth 14 are provided to extend deeper inward than an imaginary profile symmetrical with the outer flanks 15 forming the outer sides of the link teeth 14 so that they do not interfere with involute teeth of the sprocket during meshing of the chain with the sprocket.
Consequently, as shown in FIG. 5, an inner flank pitch line PL2, passing parallel to a chain pitch line PL1 (line passing over the centers of apertures 12 of the link plate 13) over the inner flanks 16 at points where the distance between the points becomes xc2xd of a chain pitch P (distance between the centers of the link apertures 12), is positioned closer to the chain pitch line PL1 than an outer flank pitch line PL3, passing parallel to the chain pitch line PL1 over the outer flanks 15 at points where the distance between those points becomes {fraction (3/2)} of the chain pitch P. That is, the profiles of the teeth of the link plate 13 are Hixe2x89xa6Ho, where Hi is a distance from the chain pitch line PL1 to the inner flank pitch line PL2, and Ho is a distance from the chain pitch line to the outer flank pitch line PL3.
Referring next to FIG. 6, the sprocket 11 has involute teeth for meshing with the silent chain. These teeth are formed by an ordinary sprocket teeth hobbing process in which a hob cutter with teeth 17 profiled correspondingly to the outer configurations of the outer flanks is used to cut a peripheral portion of the sprocket by an amount of addendum modification Hf between a gear cutting center line (tangential to a pitch radius of the sprocket) and a hob center line (tangential to an intermeshing radius of the sprocket).
It has been known that when the silent chain comprising the link plates arranged as shown in FIG. 5 is placed in meshing engagement with the sprocket having the involute teeth arranged as explained above, the silent chain is wound around the sprocket in a polygonal fashion and practically used in this manner.
However, since the link plates of the above silent chain mesh at their outer flanks alone with the involute teeth of the sprocket, the silent chain makes, upon commencement of meshing, a polygonal motion involving up and down movements radial of the sprocket.
Then, a quantitative analysis was made on the polygonal motion. As can be appreciated from FIG. 7, since a pitch angle xcex1 of the silent chain and the number of teeth N of the sprocket 11 have relations expressed by xcex1=(360xc2x0/N), the followings may be established.
First, when the chain pitch is P and a free span of the chain following the link 13b is positioned at a right angle to a line passing over the centers of the sprocket 11 and a pin 12a, the distance from the center of the sprocket 11 to the pin 12a of the chain free span is expressed by U=P/2 sin(xcex1/2). The term xe2x80x9cfree span of the chainxe2x80x9d used herein represents a chain portion not completely engaged with the sprocket but being in progress of engaging with the sprocket. In other words, the chain free span is a chain portion not completely restrained by the sprocket and is thus placed in a relatively free state.
Next, as shown in FIG. 8, when the sprocket 11 is rotated a half pitch angle xcex1/2 and the chain free span is positioned at a right angle to a line passing over the centers of the sprocket 11 and the link 13b, the distance from the center of the sprocket 11 to the chain pitch line PL1 of the chain free span is expressed by V=P/2 tan(xcex1/2).
As can be readily appreciated from the above discussion, the silent chain just started meshing engagement with the sprocket 11 makes a polygonal motion of Amplitude Hs=Uxe2x88x92V involving up and down movements during half pitch angle (xcex1/2) rotation of the sprocket 11.
Consequently, in the thus-arranged conventional power transmitting silent chain apparatus, the polygonal motion of Amplitude Hs=Uxe2x88x92V and associated up and down movements cause the link plates 13a, 13b, 13c to hit the involute teeth of the sprocket 11, resulting in an undesired beating motion. In addition, when the silent chain apparatus is operated at a high speed, undesired vibratory and impact sounds are produced at the start of meshing of the silent chain with the sprocket. Further, impact of the silent chain against the sprocket shortens the lives of the chain and the sprocket. Moreover, the polygonal motion causes the tension of the chain to change, thereby further decreasing the durability of the silent chain.
It is therefore an object of the present invention to provide a power transmitting silent chain apparatus in which vibratory sounds and impact sounds produced by up and down movements involved in the polygonal motion of the silent chain are reduced and the changes in the chain tension are alleviated, and in which the silent chain and sprocket have increased durability.
To attain the above object, there is provided, in accordance with the present invention, a power transmitting silent chain apparatus which comprises: a silent chain comprised of a plurality of link plates interconnected by connector pins, each link plate having a pair of teeth; and a sprocket having a plurality of involute teeth for meshing with the link plate teeth, the link plate teeth having inner and outer flanks profiled to satisfy the expression
Hi=Ho+Hs
where Hi is a distance from a pitch line of the chain to a pitch line of the inner flanks, Ho is a distance from the chain pitch line to a pitch line of the outer flanks, and Hs is an amplitude of a polygonal motion of the chain.
In the thus-arranged silent chain apparatus, the distance from the center of the sprocket to a free span of the chain is kept constant throughout the course of meshing of a link plate immediately before the chain free span, that is, from the start of meshing until seating on the sprocket of that link plate, thereby preventing the silent chain from making vertical movements resulting from the polygonal motion of the chain. This leads to the further advantage that vibratory sounds and impact sounds produced upon meshing of the chain with the sprocket can be alleviated and hence the silent chain apparatus is imparted with increased durability.
Preferably, engaging or bearing surfaces of the link plates are processed by shaving or fine-blanking so that they have a shear plane length of more than 70% of the thickness of the link plate. As a result, it becomes possible to reduce impact sounds produced upon meshing of the chain with the sprocket and wear of the sprocket teeth. This further prolongs the lives of the chain and sprocket and prevents stiffening of the chain links.
Each of the connector pins may comprise either a round pin or a locker pin.